Fuel supply system

This application relates to and claims priority from Japanese Patent Application No. Hei. 9-331788 filed on Dec. 2, 1997, the entire contents of which are incorporated herein by reference.

1. Field of the Invention

The present invention relates generally to fuel supply systems, and particularly to a vehicle engine fuel supply system, having a sub-tank in which a fuel pump is installed.

2. Related Art

JP-A-2-30971 discloses a fuel supply system for a vehicle engine having a fuel tank, a sub-tank in which a fuel pump is installed and a jet pump having an injection hole. In the fuel supply system, a fuel level in the sub-tank is maintained so that the fuel pump sufficiently sucks fuel from the sub-tank even when a fuel level in the fuel tank is lowered. Fuel returned from the engine is supplied to the jet pump which injects fuel into the sub-tank through the injection hole. When fuel is injected into the sub-tank, a negative pressure is generated around the injected fuel, and fuel in the fuel tank is also sucked into the sub-tank due to the negative pressure. Thus, fuel is constantly supplied to the sub-tank so that the fuel pump installed therein constantly sucks fuel from the sub-tank.

The sub-tank has a fuel inlet passage through which fuel injected by the jet pump and fuel from the fuel tank is introduced. A water head pressure corresponding to the fuel level in the sub-tank is constantly applied to the fuel inlet passage. When an amount of fuel remaining in the fuel tank is relatively large, fuel exists in a space around the injection hole of the jet pump in the fuel tank. Therefore, when fuel is injected into the fuel inlet passage by the jet pump, fuel is sucked into the fuel inlet passage due to the negative pressure and disperses over the entire cross-section of the fuel inlet passage along with the injected fuel. As a result, fuel in the sub-tank is prevented from being discharged through the fuel inlet passage toward the jet pump, and fuel in the fuel tank is introduced into the sub-tank in opposition to the water head pressure of the fuel in the sub-tank.

However, when the amount of fuel remaining in the fuel tank is decreased, and the vehicle is steered around a sharp curve or is driven on a road having a steep grade, fuel may not be dispose around the injection hole of the jet pump in the fuel tank. In this case, only fuel injected by the jet pump opposes the water head pressure of the fuel in the sub-tank. If fuel injected by the jet pump disperses insufficiently and a fuel membrane is not formed over the entire cross-section of the fuel inlet passage, fuel in the sub-tank may be discharged through a gap created between the fuel membrane and an inner wall of the fuel inlet passage. Further, if fuel is not continuously present in the space around the injection hole of the jet pump the amount of fuel in the sub-tank will greatly decrease.

Further, in the fuel supply system, a diameter of the fuel inlet passage is set relatively large (e.g., 10 mm) so that fuel in the fuel tank is spontaneously introduced into the sub-tank through the fuel inlet passage when fuel initially fills the fuel tank. When a fuel level in the fuel tank is higher than the fuel inlet passage, a gap between the injected fuel and an inner wall of the fuel inlet passage is filled with fuel. In this case, fuel is prevented from being discharged from the sub-tank although the injected fuel does not hit the inner wall of the fuel inlet passage.

Since an injection angle of fuel injected by the jet pump is relatively small, the injected fuel never contacts the inner wall of the fuel inlet passage. Therefore, when a fuel level in the fuel tank is as low as a bottom surface of the fuel tank and no fuel exists around the fuel inlet passage, a gap is created between the injected fuel and the inner wall of the fuel inlet passage. As a result, fuel in the sub-tank is discharged through the gap. Conventionally this only happens when the amount of fuel remaining in the fuel tank is extremely small. However, recently, a vehicle capable of being steered around with a maximum load with a small amount of fuel remaining in the fuel tank is in great demand. In such a vehicle, it is necessary to maintain the fuel level in the sub-tank even if the fuel level in the fuel tank is low.

The present invention is made in light of the foregoing problem, and it is an object of the present invention to provide a fuel supply system having a simple structure in which fuel is prevented from being discharged from a sub-tank even if the amount of fuel in a fuel tank decreases and fuel is not present around the injection hole of the jet pump.

It is another object of the present invention to provide a fuel supply system in which a fuel inlet passage of the sub-tank has a relatively large diameter so that fuel in a fuel tank is spontaneously introduced into the sub-tank through the fuel inlet passage, and an amount of fuel in the sub-tank is maintained even if the fuel level in the fuel tank decreases.

According to the present invention, a fuel supply apparatus has a jet pump for injecting fuel in a fuel tank to deliver fuel into a sub-tank through a fuel inlet passage by using a negative pressure generated by the such fuel injection. The jet pump has a reverse flow preventing unit for preventing fuel in the sub-tank from being discharged through the fuel inlet passage. As a result, the injected fuel uniformly disperses over an entire cross-section of the fuel inlet passage to form a fuel membrane, thereby preventing fuel from being discharged from the sub-tank. Thus, even when fuel in the fuel tank decreases and is not disposed around the injection hole of the jet pump, a fuel level in the sub-tank is maintained so that fuel is constantly supplied to the engine by the fuel pump.

According to another aspect of the present invention, the reverse flow pre venting unit has a swirl injection generating unit for generating a swirl of the fuel injection. As a result, the injected fuel uniformly disperses over an entire cross-section of the fuel inlet passage to form a fuel membrane, thereby preventing fuel from being discharged from the sub-tank.

Additional objects an d advantages of the present invention will be more readily apparent from the following detailed description of a preferred embodiment when taken together with the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view showing a fuel supply system according to a first embodiment of the present invention;

FIG. 2A is a cross-sectional view showing a jet pump and a fuel inlet passage of a sub-tank according to the first embodiment;

FIG. 2B is a partial cross-sectional view taken along line IIB--IIB in FIG. 2A showing the jet pump according to the first embodiment;

FIG. 3 is a cross-sectional view showing a part of the fuel supply system when fuel exists around the jet pump according to the first embodiment;

FIG. 4 is a cross-sectional view showing a part of the fuel supply system when fuel is not present around the jet pump according to the first embodiment;

FIG. 5 is a cross-sectional view showing a fuel supply system according to a second embodiment of the present invention;

FIG. 6 is a cross-sectional view showing a part of a jet pump according to the second embodiment; and

FIG. 7 is a cross-sectional view taken along line VII--VII in FIG. 6 showing a part of the jet pump according to the second embodiment.

Embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.

First Embodiment

As shown in FIG. 1, a fuel supply system 1 has a fuel tank 2 and a sub-tank 3 which is installed inside the fuel tank 2. A fuel pump 4 is disposed inside the sub-tank 3. A jet pump 10 is disposed outside the sub-tank 3, and is secured to the sub-tank 3 by a snap fastener or the like. The sub-tank 3 has a fuel inlet passage 3a formed at a bottom part of the sub-tank 3. Surplus fuel returned from an engine of a vehicle to the fuel tank 2 is injected by the jet pump 10 into the fuel inlet passage 3a through an injection hole 14c of the jet pump 10. When fuel is injected into the fuel inlet passage 3a from the injection hole 14c, a negative pressure is generated around the injected fuel. As a result, fuel in the fuel tank 2 is sucked into the fuel inlet passage 3a, and is introduced into the sub-tank 3 along with the injected fuel.

As shown in FIG. 2A, the jet pump 10 has a housing 11 and a lid 12 for closing the housing 11 at a rear end of the jet pump 10. The jet pump 10 has a fuel supply passage 13 through which fuel returned from the engine flows and a fuel injection passage 14. The fuel injection passage 14 has a communication portion 14a at which the fuel supply passage 13 is communicated with the fuel injection passage 14, a throttle portion 14b tapered toward a fuel downstream end of the throttle portion 14b, and the injection hole 14c formed at the fuel downstream end of the throttle portion 14b. The fuel supply passage 13 and the fuel injection passage 14 are disposed so as to be perpendicular to each other. A diameter of the communication portion 14a of the fuel injection passage 14 is larger than that of the fuel supply passage 13.

As shown in FIG. 2B, a passage axis 100 of the fuel supply passage 13 and a passage axis 101 of the fuel injection passage 14 are deviated (not on the same plane). In other words, the fuel supply passage 13 and the fuel injection passage 14 are communicated with each other so that each center axis (the passage axis 100 of the fuel supply passage 13 and the passage axis 101 of the fuel injection passage 14) do not cross each other. Further, on a hypothetical plane 102 which includes the passage axis 100 thereon, and extends across the fuel injection passage 14, an outline 13a of the fuel supply passage 13 makes contact with an outline 14d of the fuel injection passage 14.

Next, operation of the fuel supply system 1 will be described. When the engine is started and an electric current is supplied to the fuel pump 4, the fuel pump 4 sucks fuel in the sub-tank 3 and discharges the fuel outside the fuel tank 2. Surplus fuel returned from the engine is supplied to the jet pump 10 to be returned to the sub-tank 3.

According to the first embodiment, the fuel supply passage 13 and the fuel injection passage 14 in the jet pump 10 are communicated with each other so that the passage axes 100, 101 thereof do not cross each other. Therefore, fuel flowing from the fuel supply passage 13 into the communication portion 14a of the fuel injection passage 14 swirls counterclockwise. Further, as shown in FIG. 2B, fuel in the fuel supply passage 13 flows along the outlines 13a, 14d to be introduced into the fuel injection passage 14 in a manner that prevents turbulence caused by a swirling flow of fuel from occurring in the fuel injection passage 14. Further, since the diameter of the communication portion 14a of the fuel injection passage 14 is larger than that of the fuel supply passage 13, a fuel flow from the fuel supply passage 13 to the fuel injection passage 14 is not interrupted by any obstruction. Therefore, energy of fuel flowing through the fuel supply passage 13 is maintained in fuel swirling in the fuel injection passage 14. The swirling flow of fuel in the communication portion 14a is throttled in the throttle portion 14b to increase its flow rate, and is injected from the injection hole 14c with a wide injection angle so that fuel uniformly disperses without turbulence.

As shown in FIG. 3, when fuel is sufficiently supplied to the fuel tank 2 to fill a space around the injection hole 14c, and fuel is injected into the fuel inlet passage 3a of the sub-tank 3 by the jet pump 10 through the injection hole 14c, fuel in the fuel tank 2 is also sucked into the fuel inlet passage 3a due to a negative pressure generated around the injected fuel. At this time, the injected fuel and the sucked fuel from the fuel tank 2 disperses over an entire cross-section of the fuel inlet passage 3a, thereby preventing fuel in the sub-tank 3 from being discharged toward the jet pump 10 through the fuel inlet passage 3a. Further, fuel in the fuel tank 2 is introduced into the sub-tank 3 in opposition to a water head pressure of fuel in the sub-tank 3 because a pressure of the injected fuel offsets the water head pressure of fuel in the sub-tank 3. As a result, the fuel level in the sub-tank 3 is raised higher than the fuel level in the fuel tank 2 and is maintained at a predetermined level, as shown in FIG. 1.

On the other hand, when fuel in the fuel tank 2 is decreased and the vehicle is steered around a sharp curb or is driven on a road having a steep grade, fuel may not be dispose in the space around the injection hole 14c in the fuel tank 2. In this case, only fuel injected by the jet pump 10 is introduced into the fuel inlet passage 3a. However, according to the first embodiment, since the injected fuel uniformly disperses at a wide angle, a uniform fuel membrane is formed across the cross-section of the fuel inlet passage 3a. Therefore, even when fuel is not present around the injection hole 14c, fuel injected from the injection hole 14c can be introduced into the sub-tank 3 in opposition to the water head pressure of fuel in the sub-tank 3. Thus, fuel is prevented from being discharged from the sub-tank 3 through the fuel inlet passage 3a, thereby maintaining the fuel level in the sub-tank 3. (Second Embodiment)

A second embodiment of the present invention will be described with reference to FIGS. 5-7. As shown in FIG. 5, a fuel supply system 20 according to the second embodiment has a jet pump 40 disposed in a sub-tank 30. A flange portion 21 of the fuel supply system 20 is attached to a fuel tank of the fuel supply system 20. A fuel discharge port 22 and a connector 23 are integrally formed with the flange portion 21. The sub-tank 30 is attached to the flange portion 21 by a snap fastener or the like.

A fuel pump 31 is installed inside the sub-tank 30, and sucks fuel in the sub-tank 30 from a fuel inlet port 31a through a fuel filter 32. Fuel sucked by the fuel pump 31 is discharged from a fuel outlet port 31b into a branch portion 34 through a fuel filter 33. A pressure of fuel in the branch portion 34 is adjusted by a pressure regulator 35, and then separately flows into a fuel pipe 36 connected to the fuel discharge port 22 and into the jet pump 40.

The jet pump 40 has a fuel supply passage 43 and a fuel injection passage 44. The fuel having a pressure adjusted by the pressure regulator 35 flows through the fuel supply passage 43 and the fuel injection passage 44 in the jet pump 40, and is injected from an injection hole 44c of the jet pump 40, thereby generating a negative pressure around the injected fuel. As a result, fuel in the fuel tank is sucked from a fuel inlet port 30a formed in the sub-tank 30, and is introduced into a fuel inlet passage 30b formed at a bottom inner part of the sub-tank 30 together with the injected fuel. Thus, a fuel level in the sub-tank 30 is maintained higher than a fuel level in the fuel tank.

As shown in FIG. 6, a housing of the jet pump 40 is made of an outer housing 41 and an inner housing 42 inserted inside the outer housing 41. The fuel supply passage 43 and the fuel injection passage 44 are formed by the housings 41, 42, and are communicated with each other. Further, the fuel supply passage 43 and the fuel injection passage 44 are disposed to be perpendicular to each other. A diameter of the fuel injection passage 44 is larger than that of the fuel supply passage 43 at a communication point between the two passages 43, 44.

The fuel injection passage 44 has a communication portion 44a which is communicated with the fuel supply passage 43 and has a constant diameter, a throttle portion 44b tapered toward a fuel downstream end, and the injection hole 44c formed at the fuel downstream end of the throttle portion 44b. A thickness of a wall of the inner housing 42 is not uniform. The fuel supply passage 43 formed inside the inner housing 42 and an outer shape of the inner housing 42 are not co-axial. Therefore, as shown in FIG. 7, a passage axis 110 of the fuel supply passage 43 and a passage axis 111 of the fuel injection passage 44 are not on the same plane. That is, the fuel supply passage 43 and the fuel injection passage 44 are communicated with each other so that the passage axes 110, 111 thereof do not cross each other.

According to the second embodiment, fuel is injected from the injection hole 44c of the jet pump 40 at a wide injection angle, and uniformly disperses. Therefore, when fuel does not exist in a space around the injection hole 44c in the fuel tank, fuel injected from the injection hole 44c uniformly disperses over an entire cross-section of the fuel inlet passage 30b, thereby forming a fuel membrane. Therefore, fuel injected from the injection hole 44c is introduced into the sub-tank 30 in opposition to a water head pressure of fuel in the sub-tank 30. Thus, even when fuel is not present in the space around the injection hole 44c, fuel in the sub-tank 30 is prevented from being discharged from the sub-tank 30 into the fuel tank through the fuel inlet passage 30b and the fuel inlet port 30a, thereby maintaining a fuel level in the sub-tank 30.

According to the present invention, the fuel supply passage 13 and the fuel injection passage 14 in the jet pump 10 are perpendicular to each other and communicated with each other so that the passage axes 100, 101 thereof do not cross each other. Therefore, fuel flowing into the fuel injection passage 14 from the fuel supply passage 13 swirls, and the injected fuel from the injection hole 14c uniformly disperses to form a fuel membrane across the cross-section of the fuel inlet passage 3a. As a result, fuel in the fuel tank 2 continues to be introduced into the sub-tank 3 in opposition to the water head pressure of fuel in the sub-tank 3 even when fuel does not exist in the space around the injection hole 14c. Thus, fuel in the sub-tank 3 can be constantly supplied to the engine by the fuel pump 4 sufficiently.

Further, the jet pump 10 causes fuel to swirl, and has a simple structure in which the passage axes 100, 101 do not cross each other. Therefore, the jet pump 10, 40 is manufactured easily at a low production cost.

In the present invention, the diameter of the fuel injection passage 14 is larger than the diameter of the fuel supply passage 13. Therefore, fuel in the fuel supply passage 13 is smoothly introduced into the fuel injection passage 14 without being interrupted by any obstruction. As a result, an energy of fuel in the fuel supply passage 13 is maintained in fuel swirling in the fuel injection passage 14. Therefore, fuel effectively disperses at a wide angle when being injected from the injection hole 14c.

A diameter of the injection hole 14c may be decreased so that the negative pressure generated around the injected fuel is increased. In this case, the injected fuel still disperses over the cross-section of the fuel inlet passage 3a, thereby preventing fuel from being discharged from the sub-tank 3 even if fuel does not exist in a space around the injection hole 14c. Further, the diameter of the fuel inlet passage 3a of the sub-tank 3 may be increased so that fuel is more easily introduced into the sub-tank 3. In this case, by suitably designing the passages 13, 14 of the jet pump 10, fuel can be prevented from being discharged from the sub-tank 3 while the jet pump 10 sufficiently introduces fuel into the sub-tank 3. Thus, the fuel supply system design is flexible.

The fuel supply passage 13 and the fuel injection passage 14 may cross each other at a predetermined angle except 90 degrees, provided that the passage axis 100 of the passage 13 and the passage axis 101 of the passage 14 do not cross each other. The diameter of the fuel injection passage 14 may be equal to or smaller than that of the fuel supply passage 13, provided that the passage axis 100 of the passage 13 and the passage axis 101 of the passage 14 do not cross each other.

In the present invention, the jet pump 10 is formed separately from the sub-tank 3 and is disposed outside the sub-tank 3. However, the jet pump 10 may be integrally formed with the sub-tank 3.

The above discussion is also applicable to the components in the second embodiment of the present invention.

Although the present invention has been fully described in connection with preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.

Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.